名单 <string> C＃自定义排序。 在数字后加下划线

Question

I have a list: "a_a", "a1a", "aaa".

I need to sort it in following way: "a1a", "a_a", "aaa".

In other words I need '_' symbols to appear right after digits but before letters.

I know it is possible to use custom Comparer, but I haven't found any nice solution for this issue, only dirty hacks, for example:

Compare(string x, string y){

return Comparer.Default.Compare(x.Replace("_", "9z"), y.Replace("_", "9z"));

}

Answer 1

According to standard ASCII table:

  '0'..'9' have codes 0x30..0x39
  '_'      -/-        0x5F
  'a'..'z' -/-        0x61..0x7A

so since codes are in right order, you can use ordinal comparison:

  List<String> list = new List<string> {
    "a1a", "a_a", "aaa"
  };

  list.Sort((Comparison<String>) (
    (String left, String right) => {
       return String.CompareOrdinal(left, right);
    }
  ));

  ...
  // a1a, a_a, aaa
  Console.Write(String.Join(", ", list)); 

Answer 2

Here's a custom string comparer which will take a char comparer, so you can compare characters however you want. That being said, make sure StringComparer.Ordinal doesn't do the job before implementing your own comparers.

public class CustomStringComparer : IComparer<string>
{
    readonly IComparer<char> charComparer;
    public CustomStringComparer(IComparer<char> charComparer)
    {
        this.charComparer = charComparer;
    }
    public int Compare(string a, string b)
    {
        int result = 0;
        for (int i = 0; (i < a.Length || i < b.Length) && result == 0 ; i++)
        {
            if (i >= a.Length || i >= b.Length)
            {
                return i >= a.Length ? -1 : 1;
            }
            result = charComparer.Compare(a[i], b[i]);
        }
        return result;
    }
}